i've got two web apps. One was developed using Django 1.0 and the other using Django 1.4. How can I run both apps in the same apache2 server using two versions of django? Somebody told me something about virtualenv ...
I'm using mod_wsgi.

If that gives you an error, you probably don't have pip yet. You can install it using:

$ easy_install pip

Once virtualenv is installed you can create separated virtual Python environments, one per Django installation, like this:

$ virtualenv env

I recommend running this command in the project folder of each app. If you do so, you get a folder called 'env' which will contain the virtual Python environment. Every time you want to start working with the virtual environment you can issue this command:

$ source env/bin/activate

Your prompt should indicate that you are running the environment by looking something like this:

(env)$

You can leave the virtualenv by typing:

(env)$ deactivate

If you have come this far you can start installing environment-specific versions of Python packages like this (in an activated environment):

(env)$ pip install Django==1.0

This will install Django version 1.0 inside the current virtual environment. You can see if it worked by issuing:

(env)$ pip freeze

This should result in something like:

Django==1.0-final
wsgiref==0.1.2

You can now deactivate this environment, activate the other environment, and install Django 1.4 like this: